Refining apparatus or disk refiners of the above-described type are used, for instance, for highly concentrated defining, CTMP, TMP, fluffing and highly concentrated grinding of sack paper and other fibrous material containing lignocellulose. They usually comprise a rotatable refininq disk, mounted on a rotor, and a non-rotatable refining disk, mounted on a stator. Refining disks in this type of refining apparatus are built up of refining segments that form refining surfaces. The refining segments are replaced at regular intervals due to considerable wear. They are either mounted directly on the rotor and stator, respectively, or by means of special segment holders. A refining disk may consist of one or more annular refining segments or of several divided, radial refining segments. Refining segments may be in the form of central segments and peripheral segments, the peripheral segments being located outermost along the periphery, and the central segments being located inside the peripheral segments. Between the refining disk/surfaces on the rotor and stator, respectively, is a space in the form of a refining gap.
A serious problem with this type of refining apparatus is that the refined material is thrown out in the form of pulp from the refining zone, i.e. the refining gap between the refining disks, straight into the wall of the surrounding refiner housing, thus causing considerable strain on the wall, as well as substantial wear. This applies particularly when impurities in the form of clay and sand are present in the pulp, as is the case primarily with board and return fiber pulp. According to conventional technology, a special wear part is sometimes installed, suitably situated, inside the refiner housing, which is replaced at regular intervals. This naturally entails some extra expense but otherwise the housing itself would be worn out, which obviously should be avoided. One object of the present invention is primarily to remedy this problem.
Another problem is that the pulp thrown out not only causes wear on the wall of the refiner housing but may also become lodged on it and build up to a pulp cake. This occurs primarily between the rotatable parts and the refiner housing. This cake of pulp sometimes tends to become lodged and completely block transport of fibers to the outlet. Besides this obvious drawback, the build-up of pulp in the refiner housing also results in high friction along the periphery of the rotatable parts, and also considerable generation of heat which may cause the fibers to carbonize, becoming so hard that the rotor is turned as by a lathe, and may cause breakdown. Even if things do not reach this stage, the build-up of pulp causes continuous wear on the outer part of the rotor and the segment holder of the refining disk when used, so that they may break down in the end. Equivalent problems may also arise in refining apparatus of “double disk” type, i.e. having two refining disks rotatable against each other.
According to conventional technology attempts to eliminate these problems entail providing the rotor itself with wings that protrude into the space between the rotor and the wall of the refiner housing to keep it clean. However, these wings often give rise to cavitation damage in the attachment between wing and rotor, which may lead to the wing gradually becoming dislodged, with disastrous consequences.